Radiation Safety Flashcards
Dr. Edwards
Biological Effects of ionizing radiation
Energy from radiation knocks electrons out of the orbit, creating reactive elements in the body
Critical Target of Ionizing Radiation
DNA- blueprints for everything!!
Direct Effect
Ionization and destruction of DNA
Indirect Effect
production of free radicals that can then diffuse far enough to reach and damage the critical target (dna, rna, proteins)
MOST COMMON
How does x-ray cause biologic damage
can use genetic problems, cancer
damage to DNA is critical
Stem cells, young tissue
Radiosensitivity
The relative susceptibility of cells, tissues, and organs to harmful action of ionizing radiation
Radiosensitivity of Cells and Tissue Types
Stem cells are MORE radiosensitive than mature cells
Young tissue is MORE radiosensitive than old cells
Tissues with HIGH metabolic is MORE rariosensitive then low activity
Basic Principles of Radiation Safety
ALARA: As Low as Reasonably Achievable
1. Distance: Maximize distance from source (I=1/d2)
2. Time: minimize time of exposure. Limit retakes, minimize holding patients
3. Shielding: lead aprons, gloves, thyroid shields that protect from scatter beams (NOT the direct beam)
Maximum Permissible Dose of radiation
Whole body= 5,000 mrem/year
5 elements of X-ray Control Panel
mA Selector-
Focal Spot Selector -
Timer (msec)
mAs Selector (mA x time (msec))
kVp selector
Steps in producing X-ray
- Prep: electrons generated through electrical current in the filament of the cathode
- Expose: x-rays produced when electrons interact with metal in the anode
mA Selector
Controls quantity of x-rays
mAs= mA x time
Focal Spot Selector
***Controls resolution of image (quality)
Large Focal Spot: less detail or resolution
Small Focal Spot: more detail, needed for small areas such as the carpus
kVp Selector
Controls contrast of the image AND influences number of x-rays
Voltage across the x-ray tube
Higher voltage= higher e- speed= harder they hit the anode= higher beam energy
Spacial Resolution
ability to see 2 objects that are close together as being separate
Scatter Radiation
Beams that are partially absorbed by the body and then scattered into a different direction
Greater body area exposed = more scatter
Collimators
restrict beams to confined regions (usually illuminated to reduce scatter and increase contract
Grids
Prevent scatter from reaching the film
Film Vs Digital
Film: superior spatial resolution
Digital: Allows for contrast adjust which out weights benefit of spatial resolution
Radiographic opacities
Metal: Highest Attenuation- absorbs the most radiation
Bone
Soft Tissue
Fat
Air: lowest attenuation- absorbs no radiation
Degree of Attenuation
depends on the subject opacity and the thickness of the object (ex: small sliver of metal may have same degree of attenuation as a large portion of soft tissue
Summation Effect
two objects superimposed over each other have an overlapping portion that appears more opaque
(Think venn diagram)
Silhouetting Effects (Boarder Effacement)
two objects of the same subject density are in contact and appear blended together
Ex: abdominal effusion (fluid and organs have the same density so no definition can be seen)
Magnification
enlargement of an image relative to its actual size
Distortion
Unequal magnification
happens when an object is not in line with the center of the beam
Motion
causes loss of spatial resolution
DECREASED with DECREASED exposure time
Radiograph Orientation
position cranial on left side of image and caudal on right side of image for laterals
Right is on your left and left is on your right VD/DV
How to various types of electromagnetic radiation differ?
wavelength and energy. As wavelength decreases, energy increases.
Unique properties of x-ray
energy to penetrate matter.
direct engirt - breaking DNA strands
indirect- cree radicals from water into body
What determines radioactivity
varies with maturation and metabolism
immature cells -> more radiosentive
cells with higher metabolic rates are more sensitive
What is the fundamental difference in the shadow created by an x-ray beam versus a shadow
created by visible light?
visible light creates a show that outlines the outside of the object.
Xray can penetrate the object, creating multiple inter shadows all superimposed creating 2D images of internal structures
Role of collimator
restricts or limits size of x-ray beam
how does collimator improve the image
decreases scatter radiation
what is the role of the grid
limits the most of Carter radiation that reaches the detector of film
IMPORTANT FOR TEST
Which image would have been taken with a grid (A or B)
Image A would have been taken with the gird. Note the higher contrast of image A.
How do traditional film screen systems create a radiographic Image?
The function of the screens is to convert x-ray energy into visible light. It is the light
that exposes the film.
What are the 5 basic tissues densities seen on a radiograph?
Metal, bone, soft tissue, fat, air
Why is it important of have the area of interest centered in the x-ray beam?
The central portion of the x-ray beams is essentially perpendicular and there is little distortion,
where as the peripheral region of the x-ray beam diverges which can produce distortion.
Distance
Maximize your distance from radiation source
THE INVERSE SQUARE LAW!!!
Double the distance from the source will reduce exposure by 1/4
